Friction and wear are two main problems encountered during the operation of a machine. The friction is mainly influenced by the material of the friction pair, lubricating state, speed, load and so on. In practice, increasing researches have been made on the friction, and various techniques for utilizing or inhibiting the friction have been invented accordingly, for example, belt drive, rolling bearing, etc. These techniques are capable of controlling the friction passively, and the friction features of related friction components may be predetermined by specific designs and productions before use.
In the application of friction clutch, friction force of the friction parts should always been controlled during running. As passive friction controlling technique cannot fulfill the above requirements, it needs to develop an active friction controlling technique. Lots of researches have been made on the online active friction controlling technique, especially for the friction controlling technique based on an external electrical field. However, various problems still need to be solved. For example, the metal friction part is easy to corrode in the case that the lubricant is in the form of aqueous solution. When the friction is electrically controlled through an electro-chemical reaction, the metal friction part is corroded continuously due to the electro-chemical reaction. Further, when the external voltage applied on the lubricant is as high as 10-20 V, hydrogen evolution can occur in the solution. In this condition, the lubricant is significantly consumed. In the case that the lubricant is an aqueous surfactant solution, the metal friction part is easy to corrode because of immersing in the surfactant solution for a long time.
Conventional friction control techniques based on external electrical field are all limited for the reasons listed above. Currently, it is highly needed for a lubricant and a friction controlling method, which may be used in a friction controlling technique, and which are able to reduce or even avoid the corrosion of metal friction parts and may be applied within a wide load-speed range, so that requirements for the mechanical engineering can be satisfied.